<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button id="btn">btn</button>
    <script>
        var btn = document.querySelector("#btn");
        /**
         * bind
         * 箭头
        */
        // btn.onclick = function () {
        //     setTimeout(function () {
        //         console.log(this.id);
        //     }.bind(this), 500)
        // }
        btn.onclick = function () {
            setTimeout(() => {
                console.log(this.id);
            }, 500)
        }
    </script>
</body>

</html>